The present invention relates to a method and apparatus for making a rod-like filler which consists of tobacco or another smokable material. More particularly, the invention relates to improvements in a method and apparatus for making a rod-like filler from a stream which consists of shreds or otherwise configurated particles and is trimmed so as to remove the surplus whereby the remaining shreds constitute the filler. For the sake of simplicity, the invention will be described with reference to the making of rod-like fillers which consist of tobacco shreds and are intended for the mass-production of plain or filter tipped cigarettes. It is to be understood, however, that the method and apparatus can be used with equal advantage for the making of other types of rod-shaped smokers' products including cigarettes known as papyrossi as well as plain or filter tipped cigars, cigarillos and cheroots. The term "shreds" is intended to denote all types of particulate smokable material including those which are obtained by subjecting tobacco leaves, sheets of reconstituted tobacco and/or shreds of artificial tobacco to the comminuting action of orbiting knives in shredding machines, as well as constituents of smokable portions of plain or filter tipped cigars, cigarillos and cheroots.
Manufacturers of cigarettes strive to form a continuous rod-like tobacco filler which contains identical or practically identical quantities of shreds in each and every portion thereof, i.e., it is desirable to form a filler whose density is constant from increment to increment. This insures the making of cigarettes wherein the density of tobacco-containing portions matches or closely approximates a desired optimum value. As a rule, the filler is obtained by removing the surplus of tobacco from a continuous tobacco stream which contains shreds in quantities exceeding those required in the filler. The surplus is removed by a trimming or equalizing device which removes tobacco from one side of the continuously moving tobacco stream another side of which (namely, that side which is located opposite the one side) adheres to or is supported by an elongated conveyor. Adjustments in the rate of removal of tobacco from the stream are effected by moving the rotating knife or knives of the removing device toward or away from the conveyor, i.e., by varying the thickness or height of the remaining portion of the stream. The position of the knife or knives with respect to the conveyor (and more particularly the distance between the cutting plane or planes of the knife or knives and the conveyor) is regulated in response to signals which are generated by a density measuring device, for example, a beta ray detector having a source of corpuscular radiation at one side of the filler and an ionization chamber or another suitable signal generating element at the other side of the filler opposite the source. The intensity or another characteristic of signals which are transmitted by the ionization chamber is indicative of the degree of absorption of radiation by successive increments of the filler and hence of density of the corresponding portions of the filler. It is also known to resort to density measuring devices which employ means for conveying a stream of gaseous fluid transversely across the filler and an electropneumatic transducer which generates signals denoting one or more characteristics of the tobacco-modulated fluid stream, such characteristic or characteristics being indicative of the density of corresponding portions of the filler. An important advantage of fillers whose density is constant or nearly constant is that such fillers can be converted into cigarettes of predictable weight. The minimum acceptable weight of cigarettes is prescribed by authorities, and the manufacturers attempt to maintain the weight of cigarettes as close to the minimum acceptable level as possible in order to achieve savings in tobacco, i.e., in the most expensive constituent of cigarettes.
It is also known to provide the wrappers of cigarettes, especially so-called light filter cigarettes, with perforations in the form of holes which are machined into the wrappers or envelopes of filter plugs and serve to admit cool atmospheric air into the column of tobacco smoke. Thus, when the purchaser of a pack of filter cigarettes lights a cigarette, tobacco smoke is mixed with a certain amount of cool atmospheric air which enters the cigarette by way of the aforediscussed holes and influences the nicotine and condensate content of gaseous fluid which enters the smoker's mouth. It is desirable to admit a relatively high percentage of cool atmospheric air in such a way that the ratio of atmospheric air to tobacco smoke is constant from cigarette to cigarette. This ratio of cool atmospheric air to tobacco smoke in the column of gaseous fluid which issues from the free end of the filter plug is known as the degree of ventilation.
It has been found that mere regulation of density of the fillers of plain or filter tipped cigarettes cannot prevent pronounced fluctuations of the degree of ventilation, i.e, such degree is likely to vary within a wide range even if the density of each and every increment of the tobacco filler in each of a series of cigarettes equals or closely approximates a preselected optimum value. One reason for this is that the resistance which successive cigarettes of a series of such articles offer to the axial flow of a gaseous fluid (tobacco smoke or a mixture of tobacco smoke with atmospheric air) therethrough is not necessarily constant when the density of tobacco fillers in such articles is constant or identical. There are certain other factors which also influence the degree of ventilation, for example, permeability of the wrappers of plain cigarettes and/or uniting bands which connect plain cigarettes with filter plugs and the characteristics of filter plugs.